Power transmission belts having a variety of groove and rib configurations are known. One such belt is a multi-ribbed belt. The multi-ribbed belts have a tension section, a load carrying section, and a compression section. Multi-ribbed belts may also be provided with transverse grooves; such transverse grooves extending either traverse to the belt or at an angle relative to the traverse direction of the belt. The longitudinal and transverse grooves are located in the compression section. Such belts are known as cogged multi-ribbed belts, examples of which are disclosed in U.S. Pat. Nos. 4,002,082 and 5,382,198. Cogged multi-ribbed belts exhibit improved flexibility and longer life.
However, cogged multi-ribbed belts create more noise due to a non-continuous rib entering and exiting the grooved pulley. Noise is generated when the tooth travels and presses into the pulley groove, compressing and displacing the air in the groove and noise is generated when the tooth exits the pulley groove as air rushes to fill the now empty pulley groove. Furthermore, there are harmonic noise spikes generated by the cogs at the cog engagement frequency.
Two methods are known to reduce the noise of a cogged multi-ribbed belt. The first is to incline the transverse grooves at an angle relative to the transverse direction. This reduces the overall noise level but the harmonic noise spikes are often still objectionable.
The second is to vary the pitch of the cogs with a repeating pitch pattern, as disclosed by U.S. Pat. Nos. 4,264,314 and 4,832,670. U.S. Pat. No. 4,264,314 discloses a cog belt with reduced noise. The transverse groove depths, the groove angles, and the distance between the grooves are varied. Similar to U.S. Pat. No. 4,264,314, U.S. Pat. No. 4,832,670 also discloses multiple elements of the belt construction are varied simultaneously to produce a reduced noise belt. The belt is defined by a repeating sequence pattern along the length of the belt. For both belts, because of the number of variables that must be altered, construction of the belt may be more complex and costly. Also, the disclosed methods are less effective in reducing overall noise levels than inclining the transverse grooves and do not always eliminate the harmonic noise spikes.